1. Field of the Invention
This invention relates to hydraulic couplings. More particularly, it relates to undersea hydraulic couplings used in fixed volume systems.
2. Description of the Related Art
A wide variety of undersea hydraulic couplings are available. Examples of undersea hydraulic couplings having metal seals include U.S. Pat. No. 4,694,859 for “Undersea hydraulic coupling and metal seal” U.S. Pat. No. 4,817,668 for “Integral metal seal for hydraulic coupling” U.S. Pat. No. 4,884,584 for “Internally preloaded metal-to-metal seal hydraulic connector” U.S. Pat. No. 5,029,613 for “Hydraulic coupler with radial metal seal” U.S. Pat. Nos. 5,099,882 and 5,203,374 for “Pressure balanced hydraulic coupling with metal seals” U.S. Pat. No. 5,284,183 for “Hydraulic coupler with radial metal seal” U.S. Pat. No. 5,339,861 for “Hydraulic coupling with hollow metal o-ring seal” U.S. Pat. No. 5,355,909 for “Undersea hydraulic coupling with metal seals” U.S. Pat. No. 5,979,499 for “Undersea hydraulic coupling with hollow metal seal” U.S. Pat. No. 6,962,347 for “Metal backup seal for undersea hydraulic coupling” and U.S. Pat. No. 7,021,677 for “Seal retainer with metal seal members for undersea hydraulic coupling” all to Robert E. Smith III and assigned to National Coupling Company of Stafford, Tex.
Other undersea hydraulic couplings employ only “soft seals”—i.e., non-metal seals that are typically formed of an elastomeric polymer (“elastomer”) or an engineering plastic capable of being machined such as polyetheretherketone (“PEEK”) or DELRIN® acetal resin.
By way of example, U.S. Pat. No. 6,123,103 discloses a pressure balanced hydraulic coupling for use in undersea drilling and production operations. The coupling has radial passages connecting between the male and female members such that fluid pressure is not exerted against the face of either member during coupling or uncoupling. The female member has a split body with a first part and a second part, each having a longitudinal passage and a radial fluid passage. A radial seal is positioned on the junction between the first and second parts of the female member body to facilitate removal and replacement of the radial seal when the split body is disassembled. The male member may be inserted through the first and second parts of the female coupling member, thereby establishing fluid communication between the coupling members in a direction transverse to the coupling member bores.
U.S. Pat. No. 6,179,002 discloses an undersea hydraulic coupling having a radial pressure-energized seal with a dovetail interfit with the coupling body. The seal has a pair of flexible sealing surfaces for sealing with the male and female coupling members and a cavity therebetween that is exposed to fluid pressure in the coupling. The outer circumference of the seal has a dovetail interfit between inclined shoulders in the female member bore and on a seal retainer that holds the seal in the bore.
U.S. Pat. No. 6,575,430 discloses an undersea hydraulic coupling member having a ring-shaped seal with multiple scaling surfaces extending radially inwardly therefrom. The multiple sealing surfaces help guide the probe of the male coupling member into the female member without the risk of drag or galling of the receiving chamber. The seal has an interfit with reverse inclined shoulders in the female member to restrain the seal from moving radially inwardly due to vacuum or low pressure. Attention is invited in particular to the embodiments shown in FIGS. 8 and 9 of this patent.
U.S. Pat. No. 6,923,476 discloses a floating seal for an undersea hydraulic coupling member that is moveable radially to seal with the male coupling member even if there is some misalignment with the female coupling member. The floating seal is restricted from axial movement within the female coupling member receiving chamber. The floating seal may seal with the female coupling member.
U.S. Pat. No. 7,163,190 discloses a seal cartridge for an undersea hydraulic coupling member having an inner ring and an outer ring. The inner ring and outer ring are concentric and at least part of the inner ring is inserted through the outer ring. The outer ring is threaded to the coupling member and the installed seal cartridge may act to retain an elastomeric seal on a shoulder surface in the coupling member Another elastomeric seal is held between the inner ring and outer ring of the seal cartridge.
For hydraulic couplings used in undersea applications, it is common for the receiving chamber of the female coupling member to be filled with seawater before the two coupling members are joined. When the probe of the male member is inserted in the receiving chamber of the female member, it displaces the seawater in the receiving chamber. However, when the male probe is inserted sufficiently to engage the sealing members of the coupling, the seawater cannot escape and the male probe acts as a piston in a cylinder and, in the couplings of the prior art, seawater is pushed into the hydraulic system when the pressure increases to the point that the poppet valves in the coupling open.
In larger hydraulic systems, the volume of seawater that enters the system in this way is not a significant fraction of the total. However, it is generally undesirable to have seawater in a hydraulic system and, particularly in smaller systems without accumulators to compensate for the increased volume of fluid in the system, a hydraulic lock situation may occur and prevent the full mating of the coupling members. The present invention solves this problem.
U.S. Pat. No. 6,631,734 discloses a dummy undersea hydraulic coupling member for protecting an opposing undersea hydraulic coupling member when the hydraulic lines are not operating. The dummy undersea hydraulic coupling member has a water displacement expansion chamber with a piston therein that allows trapped water and/or air to move from the receiving chamber to the water displacement expansion chamber during connection of the dummy coupling member to the opposing coupling member. When the dummy coupling member is connected to an opposing coupling member subsea, seawater and/or air in the receiving chamber of the dummy is displaced by the opposing coupling member. That seawater and/or air enters the water displacement expansion chamber, and the piston allows the volume of that chamber to increase as a result of pressure from displaced seawater and/or air acting on the front face of the piston until the chamber reaches the volume required for a pressure equilibrium. When the dummy coupling member is disconnected from the opposing coupling member undersea, seawater pressure acting on the back face of the piston tends to urge the piston in a direction which decreases the volume of the water displacement expansion chamber, thus allowing the trapped seawater (and/or air) to re-enter the receiving chamber and thereby prevent a vacuum in the receiving chamber. The piston decreases the size of the water displacement expansion chamber until it reaches the volume required to establish pressure equilibrium.